1. Field of the Invention
The present invention relates to electrodeposition of ionically charged resins. More particularly, the present invention relates to electrodeposition of resins which contain a cationic charge.
2. Brief Description of the Prior Art
Electrodeposition as a coating application involves the deposition of a film-forming material under the influence of an applied electrical potential and has become of increasing commercial importance. Various resinous or polymeric film-forming materials have been developed for use in electrodeposition. Most of these resinous materials contain acid groups which are neutralized with a base such as an amine or an alkali metal hydroxide. These resin vehicles electrodeposit on the anode and because of their acidic nature tend to be sensitive to corrosive attack of alkali and salt. Further, during anionic electrodeposition, oxygen and metal ions evolved at the anode may discolor the depositing resin.
To overcome these problems, there has been a movement in the electrocoating industry to use cationically charged resins which deposit on the cathode during electrodeposition. Deposition on the cathode has the advantage over deposition on the anode in that only hydrogen is evolved at the cathode. Hydrogen evolution has no detrimental effect on the depositing resin, and in addition, cationically deposited resins frequently provide better corrosion resistance than anionically deposited resins.
An example of suitable cationic resins is found in U.S. Pat. No. 3,839,252 to Bosso et al. which discloses cationically charged resins for electrodeposition on the cathode which comprise the reaction product of a polyepoxide such as a polyglycidyl ether of a polyphenol with a tertiary amine acid salt such as the lactic acid salt of dimethylethanolamine.